Group acknowledgement for multiple user communication in a wireless local area network

ABSTRACT

In a method for simultaneously communicating with multiple communication devices in a wireless local area network a first communication device receives a plurality of uplink data units simultaneously transmitted by multiple second communication devices. The first communication device generates an acknowledgement data unit to acknowledge receipt of the multiple data units simultaneously transmitted by multiple second communication devices. The acknowledgement data unit includes (i) an indication that indicates that the acknowledgement data unit is intended for multiple second communication devices and (ii) respective acknowledgement information for the multiple second communication devices. The acknowledgement data unit is transmitted from the first communication device to the multiple second communication devices.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication entitled “GROUP ACKNOWLEDGEMENT FOR MULTIPLE USERCOMMUNICATION IN A WIRELESS LOCAL AREA NETWORK””, having a Ser. No.16/910,989, having a filing date of Jun. 24, 2020; which is acontinuation application of U.S. patent application entitled “GROUPACKNOWLEDGEMENT FOR MULTIPLE USER COMMUNICATION IN A WIRELESS LOCAL AREANETWORK”, having a Ser. No. 15/670,536, having a filing date of Aug. 7,2017; which is a continuation of U.S. patent application entitled “GROUPACKNOWLEDGEMENT FOR MULTIPLE USER COMMUNICATION IN A WIRELESS LOCAL AREANETWORK”, having a Ser. No. 14/808,932, having a filing date of Jul. 24,2015; which claims the benefit of the U.S. provisional applicationentitled “GROUP ACKNOWLEDGE DESIGN FOR UL MU MIMO/OFDMA”, having a Ser.No. 62/165,789, and having a filed date of May 22, 2015; and whichclaims the benefit of the U.S. provisional application entitled “GROUPACKNOWLEDGE DESIGN FOR UL MU MIMO/OFDMA”, having a Ser. No. 62/115,371,and having a filed date of Feb. 12, 2015; and which claims the benefitof the U.S. provisional application entitled “GROUP ACKNOWLEDGE DESIGNFOR UL MU MIMO/OFDMA”, having a Ser. No. 62/028,559, and having a fileddate of Jul. 24, 2014, having common inventors, and having a commonassignee, all of which is incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to supportboth downlink (DL) and uplink (UL) multi-user (MU) transmissions, suchas orthogonal frequency division multiple access (OFDMA) transmissionsand multi-user multiple input multiple output (MU-MIMO) transmissions,and to provide even greater throughputs, such as throughputs in the tensof Gbps range.

SUMMARY

In an embodiment, a method for simultaneously communicating withmultiple communication devices in a wireless local area network includesreceiving, at a first communication device, a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices. The method also includes generating, at the first communicationdevice, an acknowledgement data unit to acknowledge receipt of themultiple data units simultaneously transmitted by multiple secondcommunication devices, wherein the acknowledgement data unit includes(i) an indication that indicates that the acknowledgement data unit isintended for multiple second communication devices and (ii) respectiveacknowledgement information for the multiple second communicationdevices. The method additionally includes causing the acknowledgementdata unit to be transmitted from the first communication device to themultiple second communication devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN), according to an embodiment;

FIG. 2 is a diagram of an example data unit, according to an embodiment;

FIG. 3 is a diagram of an example transmission sequence in a WLAN,according to an embodiment;

FIG. 4 is a diagram of an other example transmission sequence in a WLAN,according to another embodiment;

FIG. 5 is a diagram of an example an example acknowledgement frame,according to an embodiment;

FIG. 6 is a diagram of an example control field of an acknowledgementframe, according to an embodiment;

FIG. 7 is a diagram of an information element included in anacknowledgement frame, according to an embodiment;

FIG. 8A is a diagram of an example subfield of an information field ofan acknowledgement frame, according to an embodiment;

FIG. 8B is a diagram of an other example subfield of an informationfield of an acknowledgement frame, according to another embodiment;

FIG. 9 is a flow diagram of an example method that is implemented by anAP in a WLAN, according to an embodiment; and

FIG. 10 is a flow diagram of an example method that is implemented by anAP in a WLAN, according to another embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) simultaneouslytransmits independent data streams to multiple client stations and/orreceives independent data streams simultaneously transmitted by multipleclient stations. For example, the AP transmits data for the multipleclients in different orthogonal frequency division multiplexing (OFDM)sub-channels of an orthogonal frequency division multiple access (OFDMA)transmission, in an embodiment. Similarly, multiple client stationstransmit data to the AP simultaneously, in particular, each clientstation transmits data in a different OFDM sub-channel of an OFDMAtransmission, in an embodiment. In another embodiment, the AP transmitsdata for multiple client stations using different spatial streams of amulti-user multiple input multiple output (MU-MIMO) transmission.Similarly, multiple client stations transmit data to the APsimultaneously using different spatial streams within an MU-MIMIOtransmission to the AP, in an embodiment.

In an embodiment, upon receiving simultaneous transmissions frommultiple client stations, the AP acknowledges receipt of thesimultaneous transmissions by transmitting one or more acknowledgementframes to the client stations. For example, in an embodiment, the APtransmits an OFDMA acknowledgement frame that includes respectiveacknowledgements intended for different client stations in differentOFDM sub-channels, in an embodiment. In another embodiment, the APtransmits an MU-MIMO acknowledgment frame that includes respectiveacknowledgements intended for different client stations transmitted indifferent spatial streams. In yet another embodiment, the AP transmits abroadcast acknowledgement frame that is broadcast to the multiple clientstations and includes the respective acknowledgements intended for themultiple client stations, or a multicast acknowledgement frame that ismulticast to the multiple client stations and includes the respectiveacknowledgements intended for the multiple client stations. The APacknowledges receipt of simultaneous transmissions from multiple clientstations in other suitable manners, in other embodiments.

The AP is configured to operate with client stations according to atleast a first communication protocol. The first communication protocolis sometimes referred to herein as “high efficiency WiFi,” “highefficiency WLAN,” “HEW” communication protocol, or IEEE 802.11axStandard. The first communication protocol supports OFDMA communicationbetween the AP and the client stations. In some embodiments, differentclient stations in the vicinity of the AP are configured to operateaccording to one or more other communication protocols that defineoperation in the same frequency band as the HEW communication protocolbut with generally lower data throughputs. The lower data throughputcommunication protocols (e.g., IEEE 802.11a, IEEE 802.11g, IEEE 802.11n,and/or IEEE 802.11ac) are collectively referred herein as “legacy”communication protocols. The legacy communication protocols do notsupport OFDMA communication, in an embodiment.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1 , the AP 14 includes differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1 , the WLAN 10 includesdifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. Two or more of the client stations 25are configured to receive corresponding data streams that aretransmitted simultaneously by the AP 14. Addition ally, two or more ofthe client stations 25 are configured to transmit corresponding datastreams to the AP 14 such that the AP 14 receives the data streamssimultaneously.

A client station 25-1 includes a host processor 26 coupled to a networkinterface 27. The network interface 27 includes a MAC processing unit 28and a PHY processing unit 29. The PHY processing unit 29 includes aplurality of transceivers 30, and the transceivers 30 are coupled to aplurality of antennas 34. Although three transceivers 30 and threeantennas 34 are illustrated in FIG. 1 , the client station 25-1 includesdifferent numbers (e.g., 1, 2, 4, 5, etc.) of transceivers 30 andantennas 34 in other embodiments.

In an embodiment, one or more of the client stations 25-2, 25-3, and25-4 has a structure the same as or similar to the client station 25-1.In these embodiments, the client stations 25 structured like the clientstation 25-1 have the same or a different number of transceivers andantennas. For example, the client station 25-2 has only two transceiversand two antennas (not shown), according to an embodiment.

According to an embodiment, the client station 25-4 is a legacy clientstation that is not enabled to receive a data stream that is transmittedby the AP 14 simultaneously with other independent data streams as partof an OFDMA transmission to multiple client stations 25. Similarly,according to an embodiment, the legacy client station 25-4 is notenabled to transmit a data stream that to the AP 14 as part of OFDMAtransmission from multiple client stations 25. According to anembodiment, the legacy client station 25-4 includes a PHY processingunit that is generally capable of receiving a data stream that istransmitted by the AP 14 simultaneously with other independent datastreams that are intended for other client stations 25. But the legacyclient station 25-4 includes a MAC processing unit that is not enabledwith MAC layer functions that support receiving the data stream that istransmitted by the AP 14 simultaneously with other independent datastreams that are intended for other client stations 25. According to anembodiment, the legacy client station 25-4 includes a PHY processingunit that is generally capable of transmitting a data stream to the AP14 at the same time that other client stations 25 transmit data to theAP 14. But the legacy client station 25-4 includes a MAC processing unitthat is not enabled with MAC layer functions that support transmitting adata stream to the AP 14 at the same time that other client stations 25transmit data to the AP 14.

FIG. 2 is a diagram of a physical layer data unit 200, according to anembodiment. The AP 14 is configured to transmit to a client station(e.g., the client stations 25-1) via orthogonal frequency domainmultiplexing (OFDM) modulation, according to an embodiment. In anembodiment, the client station 25-1 is also configured to transmit thedata unit 200 to the AP 14. The data unit 200 conforms to the HEWcommunication protocol, in the illustrated embodiment. The data unit 200conforms to a legacy communication protocol such as the IEEE 802.11aStandard, the IEEE 802.11g Standard, the IEEE 802.11n Standard or theIEEE 802.11ac Standard, in some embodiments. In such embodiments, one ormore fields of the data unit 200 is/are replaced by corresponding fieldsthat conform to the legacy communication protocol.

The data unit 200 includes a preamble 202, which, in turn, includes alegacy preamble portion 203 and a high efficiency (HE) preamble portion204. The legacy preamble portion 202 includes an L-STF 205, an L-LTF210, and an L-SIG 215. The HE preamble portion 204 includes one or moreHE signal field (s) (HE-SIGA (s)) 220, an HE short training field(HE-STF) 225, MHE long training fields (HE-LTFs) 230, where M is aninteger, and an HE signal field B (HE-SIGB) 235. Each of the L-STF 205,the L-LTF 210, the L-SIG 215, the HE-SIGAs 220, the HE-STF 225, the MHE-LTFs 230, and the HE-SIGB 235 comprises an integer number of one ormore OFDM symbols. For example, in an embodiment, the HE-SIGAs 220comprise two OFDM symbols, and the HE-SIGB field comprises one OFDMsymbol, in an embodiment. The L-SIG 215, the HE-SIGAs 220 and theHE-SIGB 235 generally carry formatting information for the data unit200, in an embodiment. The data unit 200 also includes a data portion240.

According to an embodiment, each of the L-STFs 205 and each of theL-LTFs 210 have a format as specified in a legacy protocol such as theIEEE 802.11a Standard, the IEEE 802.11g Standard, the IEEE 802.11nStandard, and/or the IEEE 802.11ac Standard. In an embodiment, each ofthe L-SIGs 215 has a format at least substantially as specified inlegacy protocol (e.g., the IEEE 802.11a Standard, the IEEE 802.11gStandard, the IEEE 802.11n Standard, and/or the IEEE 802.11ac Standard),In such embodiments, the length and rate subfields in the L-SIGs 215 isset to indicate the duration T corresponding to the remainder of thedata unit 200 after the legacy portion. This permits client stationsthat are not configured according to the HEW protocol to determine anend of the data unit 200 for carrier sense multiple access/collisionavoidance (CSMA/CA) purposes, for example. For example, the legacyclient stations determine the duration of the remainder of the data unit200 and refrain from accessing the medium (or at least transmitting inthe medium) for the duration of the remainder of the data unit 200, inan embodiment. In other embodiments, each of the L-SIGs 215 has a formatat least substantially as specified in legacy protocol (e.g., the IEEE802.11a Standard, the IEEE 802.11g Standard, the IEEE 802.11n Standard,and/or the IEEE 802.11ac Standard) but with length field in the L-SIGs225 set to indicate a duration of the time remaining in a transmissionopportunity (TXOP) during which the data unit 200 is transmitted. Insuch embodiments, client stations that are not configured according tothe HEW protocol determine an end of the TXOP and refrain from accessingthe medium (or at least transmitting in the medium) for the duration ofthe TXOP. Thus, the medium is protected from transmissions by a legacyclient station for the duration of the TXOP even if the legacy clientstation that does not support MU-MIMO and OFDMA communication and cannotdecode, or determine duration of, data units that are transmittedsubsequent to transmission of the data unit 200 using MU-MIMO or OFDMAtransmissions, in an embodiment.

In an embodiment, the HE-preamble portion 204 at least substantiallyconforms to a legacy communication protocol, such as the IEEE 802.11acStandard. In another embodiment, the HE-preamble portion 204 conforms tothe first communication protocol but does not conform to any legacycommunication protocol. For example, the HE-preamble portion 204includes a higher number of OFDM symbols in one or more of the HE-SIGAfield 220, the HE-STF field 225, each of the HE-LTF fields 230 and theHE-SIGB as compared to the corresponding fields defined by any legacycommunication protocol.

In the embodiment of FIG. 2 , the data unit 200 occupies a 20 MHzbandwidth and includes one of each of the L-STF 205, the L-LTF 210, theL-SIG 215, and the HE-SIGA (s) 220. In other embodiments in which anOFDM data unit similar to the data unit 200 occupies a cumulativebandwidth other than 20 MHz, each of the L-STF 205, the L-LTF 210, theL-SIG 215, the HE-SIGA (s) 220 is repeated over a corresponding numberof 20 MHz sub-bands of the whole bandwidth of the data unit, in anembodiment. For example, in an embodiment, the OFDM data unit occupiesan 80 MHz bandwidth and, accordingly, includes four of each of the L-STF205, the L-LTF 210, the L-SIG 215, and the HE-SIGA (s) 220. In someembodiments, the modulation of different 20 MHz sub-bands signals isrotated by different angles. For example, in one embodiment, all OFDMtones within a first subband are rotated 0-degrees, all OFDM toneswithin a second subband is rotated 90-degrees, a third sub-band isrotated 180-degrees, and a fourth sub-band is rotated 270-degrees. Inother embodiments, different suitable rotations are utilized. Thedifferent phases of the 20 MHz sub-band signals result in reduced peakto average power ratio (PAPR) of OFDM symbols in the data unit 200, inat least some embodiments. In an embodiment, if the data unit thatconforms to the first communication protocol is an OFDM data unit thatoccupies a cumulative bandwidth such as 20 MHz, 40 MHz, 80 MHz, 160 MHz,320 MHz, 640 MHz, etc., the HE-STF, the HE-LTFs, the HE-SIGB and the HEdata portion occupy the corresponding whole bandwidth of the data unit.

FIG. 3 is a diagram of an example transmission sequence 300 in a WLAN,such as the WLAN 10 of FIG. 1 , according to an embodiment, in which anAP, such as the AP 14, prompts multiple client stations, such asmultiple ones of the client stations 25, to transmit independent datasimultaneously to the AP during a transmission opportunity (TXOP) 302.The AP 14 generates and transmits a communication frame 304 that promptsthe multiple client stations to transmit independent data simultaneouslyto the AP during the TXOP 302, in an embodiment. In an embodiment, thecommunication frame 304 is a management frame or a control frame, suchas a synchronization (SYNC) frame. In an embodiment, the communicationframe 304 prompts multiple client stations in an MU-MIMO group of clientstations to simultaneously transmit independent data to the AP usingrespective spatial streams. In another embodiment, the communicationframe 304 prompts multiple client stations in an OFDMA group of clientstations to simultaneously transmit independent data to the AP usingrespective OFDM subchannels.

In an embodiment, the communication frame 304 occupies a bandwidth of aprimary channel (e.g., a primary 20 MHz channel) of the WLAN 10. In anembodiment, the AP 14 transmits the communication frame 304 in theprimary channel of the WLAN 10. In an embodiment, the AP 14 furtherduplicates the communication frame 304, and transmits a duplicatedcommunication frame 304 in each channel (each 20 MHz channel) of theWLAN 10. The communication frame 304 indicates, to the multiple clientstations 25, which spatial stream or streams, or which OFDM channel orchannels, is/are allocated to each of the multiple client stations 25,in an embodiment. Addition ally or alternatively, the communicationframe 304 indicates other transmission parameters to the multiple clientstations 25, such as which modulation and coding scheme (MCS) each ofthe client stations should use, the OFDM numerology (e.g., guardinterval, tone spacing, etc.) that each of the multiple client stationsshould use, transmit power that each of the multiple client stations 25should use, etc. In an embodiment, the communication frame 304 isformatted according to the physical layer data unit (PPDU) formatspecified in the IEEE 802.11a Standard, the IEEE 802.11g Standard, IEEE802.11n Standard and/or IEEE 802.11ac Standard. In an embodiment, thecommunication frame 304 corresponds to the data unit 200 of FIG. 2 . Inanother embodiment, the communication frame 304 is a suitable data unitdifferent from the data unit 200 of FIG. 2 .

In response to receiving the communication frame 304, the multipleclient stations transmit independent data simultaneously to the AP 14during the TXOP 302. For example, the multiple client stations 25transmit respectively data units 306 to the AP 14 as parts of amulti-user uplink transmission 308 to the AP 14, in an embodiment. Eachdata unit 306 includes a MAC protocol data unit (MPDU) from thecorresponding client station 25 to the AP 14 or an aggregated MDPU(A-MPDU), that includes multiple MPDUs, from the corresponding clientstation 25 to the AP 14, in various embodiments. In an embodiment, theuplink transmission 308 is an MU-MIMO transmission from the clientstations 25 to the AP 14. In this embodiment, the client stations 25transmit the respective data units 306 using respective one or morespatial streams allocated to the client stations 25. In an otherembodiment, the uplink transmission 308 is an OFDMA transmission fromthe client stations 25 to the AP 14. In this embodiment, the clientstations 25 transmit the respective data units 306 using respective OFDMsubchannels allocated to the client stations 25.

In response to receiving the uplink transmission 308 from the clientstations 25, the AP 14 generates and transmits multiple acknowledgementdata units 310 that include respective acknowledgment frames (Acks orBlockAcks (BAs)) to acknowledge data units 306 received from the clientstations 25. In the embodiment shown in FIG. 3 , the AP transmitsseparate independent acknowledgement data units 310 the multiple clientstation 25 as parts of a multi-user (MU) downlink acknowledgement dataunit 312 to the client stations 25. In an embodiment, the downlink MUacknowledgement data unit 312 is an MU-MIMO data unit transmitted fromthe AP 14 to the multiple client stations 25. In this embodiment, the AP14 transmits respective acknowledgement data units 310 to the clientstations 25 using respective spatial streams allocated to the clientstations 25. For example, in an embodiment, the AP 14 transmits theacknowledgement data units 310 to respective client stations 25 usingthe same spatial streams as the spatial streams in which thecorresponding data units 306 were transmitted to the AP 14, in anembodiment. In an embodiment in which the downlink MU acknowledgementdata unit 312 is an MU-MIMO transmission from the AP 14 to the multipleclient stations 25, the AP 14 conducts a suitable beamforming trainingprocedure (s) with the multiple client stations 25 prior to transmittingthe downlink MU acknowledgement data unit 312, and, based on thebeamforming training, beamforms transmission of the downlink MUacknowledgement data unit 312 to the multiple client stations 25.

In an other embodiment, the downlink MU acknowledgement data unit 312 isan OFDMA data unit transmitted from the AP 14 to the multiple clientstations 25. In this embodiment, the AP 14 transmits respectiveacknowledgement data units 310 to the client stations 25 usingrespective OFDM subchannels allocated to the client stations 25. Forexample, in an embodiment, the AP 14 transmits the acknowledgement dataunits 310 to respective client stations 25 using the same OFDMsubchannels as the OFDM subchannels in which the corresponding dataunits 306 were transmitted to the AP 14, in an embodiment. In anotherembodiment, the AP 14 transmits the acknowledgement frames 310 torespective client stations 25 using different OFDM subchannels ascompared to at least some of the OFDM subchannels in which thecorresponding data units 306 were transmitted to the AP 14. In someembodiments, the downlink MU acknowledgement data unit 312 is an OFDMAdata unit transmitted from the AP 14 to the multiple client stations 25even if the data units 306 were transmitted to the AP 14 as parts of anMU-MIMO transmission to the AP 14 (i.e., even if the uplink transmission308 is an MU-MIMO transmission from the client stations 25 to the AP14).

Although in the embodiment illustrated in FIG. 3 only one communicationframe 304, only one uplink transmission 308 and only one MUacknowledgement data unit 312 are transmitted during the TXOP 302,multiple communication frames 304, multiple uplink transmissions 308and/or multiple acknowledgement data units 312 are transmitted duringthe TXOP 302, in some embodiments. For example, in an embodiment, thecommunication frame 304 prompts the multiple client stations 25 totransmit multiple uplink data units during the TXOP 302. As anotherexample, in an embodiment, an additional communication frame 304,transmitted during the TXOP 302, subsequent to transmission of thedownlink acknowledgement data nit 312, prompts the multiple clientstations 25 to simultaneously transmit additional uplink data units 306to the AP 14, in some embodiments. Transmission of the additional uplinkdata units 306 is followed by transmission of additional downlinkacknowledgement data units 310 to acknowledge the additional uplink dataunits 306, in an embodiment.

In some embodiments, the TXOP 302 includes transmission of one or moreMU downlink transmissions, such as one or more downlink OFDMAtransmissions or one or more downlink MU-MIMO transmissions, from the AP14 to the client stations 25, in addition to the uplink transmission 308from the multiple client stations 25 to the AP 14. For example thecommunication frame 304 indicates that a downlink transmission to themultiple client stations 25 will follow the uplink transmission receivedfrom the client stations 25, in an embodiment. Alternatively, anadditional communication frame 304, transmitted during the TXOP 302,subsequent to transmission of the downlink acknowledgement data nit 312,indicates that an MU downlink transmission to the multiple clientstations 25 will follow the additional communication frame 304, in someembodiments. In an embodiment, the MU downlink transmission to themultiple client stations 25 includes respective downlink data unitshaving independent data transmitted to the multiple client stations 25.

In some embodiments, the acknowledge data units 310 are included in, orcombined with, a multi-user (e.g., MU-MIMO of OFDMA) downlink datatransmission from the AP 14 to the client stations 25 during the TXOP302. For example, in an embodiment, the communication frame 304indicates a downlink multi-user (e.g., OFDMA) transmission to themultiple client stations 25 during the TXOP 302, that will follow theuplink MU transmission triggered by the communication frame 304.Alternatively, after receiving the uplink transmission 308, the AP 14transmits another communication frame such as the communication frame304 to trigger a downlink multi-user (e.g., OFDMA) transmission to themultiple client stations 25 to take place during the TXOP 302, in anembodiment. The AP 14 then includes the acknowledge data units 310 inthe downlink OFDMA transmission to the client stations 25, in suchembodiments. That is, in such embodiments, the downlink multi-usertransmission includes both (i) respective acknowledgement data units 310that carry acknowledgement information to the client stations 25 and(ii) respective data units, such as respective A-MPDUs, that carry datafor the client stations 25.

In an embodiment, the acknowledgement data units 310 are not necessaryof equal length. For example, in an embodiment, each of theacknowledgement data units 310 includes one of (i) an acknowledgement(Ack) frame that acknowledges a data unit 306 that included a singledata unit, such as a single MPDU or (ii) a block acknowledgement(BlockAck or BA) frame that acknowledges a data unit 306 that includedmultiple data units, such as multiple aggregated MPDUs. Anacknowledgement frame 306 that include an Ack frame is shorter than anacknowledgement data unit 310 that includes a BlockAck frame, in anembodiment. Additionally or alternatively, in some embodiments, the AP14 transmits at least some of the acknowledgement data units 310 usingdifferent bandwidths, different data rates and/or different modulationand coding schemes as compared to other ones of the acknowledgement dataunits 310. Different bandwidths, data rates and/or modulation and codingschemes of the acknowledgement data units 310 results in differentlengths or time durations of the acknowledgement data units 310, in anembodiment. In an embodiment, the AP 14 pads one or more of theacknowledgement data units 310, using a suitable padding technique, toequalize the lengths of the acknowledgement data units 310. As merely anexample, AP 14 pads one or more of the acknowledgement data units 310using MAC and/or PHY padding techniques specified in the IEEE 802.11acStandard, in an embodiment.

In an embodiment, the AP 14 selects different data rates and/ormodulation and coding schemes to be used for transmission of differentacknowledgement data units 310, in an embodiment. In an embodiment, theAP selects a suitable data rate and/or modulation and coding scheme foreach of the acknowledgment data units 310 based on capabilities of theclient station 25 that is the intended recipient of the acknowledgementdata units 310. For example, the AP 14 selects, for each of theacknowledgement data units 310, a suitable modulation and coding schemesupported by the client station 25 that is the intended recipient of theacknowledgement data units 310 as long as the resulting time duration oftransmission of the acknowledgement data units 310 does not exceed themaximum time duration allotted for the transmission of the MU data unit312, in an embodiment.

In an embodiment, the AP 14 transmits a suitable data unit in place ofone or more of the acknowledgement data units 310 in case the AP 14 didnot receive corresponding one or more data units 306 in the uplinktransmission 308. For example, the AP 14 does not receive a data unit306 from a client station 25 that was prompted by the communicationframe 304, in some scenarios. The AP 14 then transmits a data unit, suchas a quality of service (QoS) Null frame, an MPDU delimiter, or anothersuitable frame, in place of the corresponding acknowledgement data units310 to the client station 25, in an embodiment.

FIG. 4 is a diagram of another example transmission sequence 400 in aWLAN, such as the WLAN 10 of FIG. 1 , according to an embodiment. Thetransmission sequence 400 is generally the same as the transmissionsequence 300 of FIG. 3 , however the AP 14 transmits a singleacknowledgement data unit 416 that includes a broadcast or a multicastacknowledgement data unit 416 transmitted to multiple client stations 25instead of multiple acknowledgement data units 310 that include separateacknowledgment frames transmitted to each of the multiple clientstations 25. In an embodiment, the acknowledgement data unit 416includes a broadcast or a multicast acknowledgement frame that the AP 14transmits to the client stations 25 from which the data units 306 werereceived. In an embodiment, the acknowledgement data unit 416 includes abroadcast MAC address. In an embodiment, the acknowledgement data unit416 includes the group ID of the client uplink group (e.g., as areceiver address), station identifiers (e.g., association identifiers(AIDs) or partial AIDs) from which the data units 306 were transmitted,and/or other suitable acknowledgment information which acknowledges thetransmissions from the multiple client stations 25. In an embodiment,the acknowledgement data unit 416 corresponds to the data unit 200 ofFIG. 2 . In another embodiment, the acknowledgement data unit 416 is asuitable data unit different from the data unit 200 of FIG. 2 .

In an embodiment, the acknowledgement data unit 416 includes Ackinformation and BlockAck (BA) information to acknowledge MPDU or A-MPDUtransmissions, respectively, from respective ones of the client stations25. In an embodiment, the AP 14 transmits the acknowledgement data unit416 in a single OFDM channel and/or in a single spatial stream. Forexample, in an embodiment, the AP 14 transmits the acknowledgement dataunit 416 in the OFDM channel in which the uplink transmission 308 wastransmitted to the AP 14. In this embodiment, the acknowledgement dataunit 416 occupies the bandwidth that was cumulatively occupied by thedata units 306 being acknowledged by the AP 14 (e.g., bandwidth of thetransmission 308 to the AP 14), In an embodiment in which theacknowledgement data unit 416 occupies the bandwidth that wascumulatively occupied by the data units 306 being acknowledged by the AP14, the acknowledgement data unit 416 may be shorter (e.g., intransmission time) for example compared to a system in which theacknowledgement data unit 416 occupies the bandwidth of a primarychannel of the WLAN 10. In an other embodiment, the AP 14 duplicates theacknowledgement data unit 416 in each OFDM channel, such as each 20 MHzchannel within the bandwidth that was cumulatively occupied by the dataunits 306 being acknowledged by the AP 14. In such embodiments, theclient stations 25 receiving the acknowledgement data unit 416 cancombine the duplicated acknowledgement data units 416, for example toimprove reception performance. In an embodiment, the acknowledgementdata unit 416 is a physical layer protocol data unit (PPDU) formattedaccording to a legacy PPDU format, such as a PPDU format specified inthe IEEE 802.11a Standard or an IEEE 802.11g Standard. In thisembodiment, a legacy client station, such as the client station 25-4,can decode the acknowledgement data unit 416, and can obtain a durationof the acknowledgement data unit 416 from duration information includedin a MAC header within the acknowledgement data unit 416. In anotherembodiment, the acknowledgement data unit 416 is a physical layerprotocol data unit (PPDU) formatted according to a new format defined inthe first communication protocol (e.g., a high efficiency (HE) PPDUformat). The new PPDU format is used to transmit the acknowledgementdata unit 416, for example, in outdoor or extended range communicationchannel in which the VHT format may result in an insufficient receptionquality, in some embodiments. In some embodiments, the acknowledgementdata unit 416 is combined with other transmission, such as an aggregatemedia access control protocol data unit (A-MPDU) or a SYNC communicationframe subsequently transmitted to the client stations 25, during theTXOP 302.

In an embodiment, the AP 14 selects, from a set of available data ratesand/or modulation and coding schemes (MCSs), a data rate and/or amodulation and coding scheme (MCS) to be used for transmission of theacknowledgement data unit 416. In an embodiment, the AP 14 selects thedata rate and/or the coding scheme from a basic rate set of a basicservice set (BSSBasicRateSet) of a BSS served by the AP 14. In anembodiment, the AP 14 selects any suitable data rates and/or anysuitable MCS from the set of available data rate and/or MCSs, such asfrom the BSSBasicRateSet. Alternatively, in an embodiment, the AP 14selects any suitable data rates and/or any suitable MCS from a set ofavailable data rate and/or MCSs from a mandatory rate set supported bythe PHY processing unit 20 of the AP 14. For example, the AP 14 selectsany suitable data rates and/or any suitable MCS from a set of availabledata rate and/or MCSs from a mandatory rate set supported by the PHYprocessing unit 20 of the AP 14 when the BSSBasicRateSet is empty oridle, in an embodiment.

In at least some embodiments and/or scenarios, the AP 14 selects a datarate, an MCS, and/or Nss for transmission of the acknowledgement dataunit 416 without considering the data rates and/or modulation and codingschemes with the data units 306 were transmitted to the AP 14. In atleast some embodiments and/or scenarios, the AP 14 selects a data ratethat is greater than the lowest data rate or MCSs among the data ratesor MCSs of the data units 306. In another embodiment, the AP 14considers the data rates and/or modulation and coding schemes, with thedata units 306 were transmitted to the AP 14, when determining a datarate and/or an MCS for transmission of the acknowledgement data unit416. For example, the AP 14 selects a highest available data rate and/orMCS that is less than or equal to the lowest data rate and/or MCSs amongthe data rates and/or MCSs of the data units 306.

In an embodiment, the AP 14 selects a data rate, a modulation and codingscheme (MCS), and/or a number of spatial streams (Nss) for transmissionof the acknowledgement data unit 416 from a set of data rates and/ormodulation and coding schemes that are supported by the client stations25 to which the acknowledgement data unit 416 is directed. As anexample, in an embodiment in which the acknowledgement data unit 416 isa non-HT data unit, such as a data unit that conforms to the IEEE802.11a Standard, the AP 14 selects, for transmission of theacknowledgement data unit 416, a data rate from a set of data ratessupported by the client stations 25 that are the intended recipients ofthe acknowledgement data unit 416. As another example, in an embodimentin which the acknowledgement data unit 416 is an HT data unit, such as adata unit that conforms to the IEEE 802.11n Standard, the AP 14 selects,for transmission of the acknowledgement data unit 416, an MCS from a setof MCSs supported by the client stations 25 that are the intendedrecipients of the acknowledgement data unit 416. As another example, inan embodiment in which the acknowledgement data unit 416 is a VHT dataunit, such as a data unit that conforms to the IEEE 802.11ac Standard,the AP 14 selects, for transmission of the acknowledgement data unit416, an MCS and Nss from a set of MCSs/Nss supported by the clientstations 25 that are the intended recipients of the of theacknowledgement data unit 416. As yet another example, in an embodimentin which the acknowledgement data unit 416 is an HE data unit, such as adata unit that conforms to the IEEE 802.11ax Standard, the AP 14selects, for transmission of the acknowledgement data unit 416, an MCSand Nss from a set of MCSs/Nss supported by the client stations 25 thatare the intended recipients of the of the acknowledgement data unit 416.In at least some such embodiments, the AP 14 selects, for transmissionof the acknowledgement data unit 416, a data rate, and MCS and/or Nssthat is/are higher than the corresponding parameters used fortransmission of the data units 306 being acknowledged by theacknowledgement data unit 416. In such embodiments, transmission time ofthe acknowledgement data unit 416 may be reduced compared to systems inwhich selection of data rate, and MCS and/or Nss is limited by the datarate, MCS and/or Nss used for transmission of the data units 306.

In some embodiments, other client stations 25 in the WLAN 10 may beunable to decode the entire acknowledgement data unit 416 if such otherclient stations 25 do not support the data rate, MCS and/or Nss selectedfor transmission of the acknowledgement data unit 416. Accordingly, aclient station 25 that cannot decode the entire acknowledgement dataunit 416 is unable to set its navigation allocation vector (NAV) basedon a duration indicated within a header (e.g., MAC header) included inthe acknowledgement data unit 416. However, in an embodiment in whichthe acknowledgement data unit 416 is an HE data unit, a non-legacyclient station 25 that supports the HE communication protocol (“HEclient station”) is able to set its NAV based on a duration indicationincluded in a signal field of a preamble of the acknowledgement dataunit 416 even if the non-legacy client station does not support the datarate, MCS and/or Nss selected for transmission of the acknowledgementdata unit 416, in an embodiment.

Referring to FIG. 2 , in an embodiment, the HE-SIGA field 220 or theHE-SIGB field 235 included in the acknowledgement data unit 416 includesa duration indication that indicates a remaining duration of the TXOP302 after transmission of the acknowledgement data unit 416, in anembodiment. In an embodiment, an HE client stations 25 that is that isnot a participant in the TXOP 302, such as an HE client station 25 thatis not a member of an MU-MIMO group or an OFDMA group indicated by thecommunication frame 304, sets its NAV based on a duration indication inthe HE-SIGA field 220 or the HE-SIGB field 235 included in theacknowledgement data unit 416. A legacy station 25, however, isgenerally not able to decode the duration indication in the HE-SIGAfield 220 or the HE-SIGB field 235 included in the acknowledgement dataunit 416. In an embodiment, the communication frame 304 that triggerstransmission of the data units 306 is decodable by legacy clientstations, and includes a duration indications (e.g., in the HE-SIGAfield 220 or the HE-SIGB field 235 included in the communication frame304) that indicates a remaining duration of the TXOP 302 aftertransmission of the communication frame 304, in an embodiment. A legacyclient station 25 sets its NAV based on the duration indication in thecommunication frame 304, in an embodiment Accordingly, transmission ofthe acknowledgement data unit 416 is protected from transmissions byclient stations 25 that are not intended participants in the TXOP 302even if such client stations 25 are unable to decode the acknowledgementdata unit 416, in an embodiment.

In an embodiment, if a client station 25 detects an error in receptionof the acknowledgement data unit 416, then the client station 25 cannotits NAV and instead sets its backoff timer to a duration of an extendedinterframe space (EIFS), and, accordingly, refrains from accessing themedium for the duration of EIFS. If the acknowledgement data unit 416 isthe not the last frame in transmitted in the TXOP 302, then the backofftimer, set to the duration of EIFS based on detection of an error in theacknowledgement frame 402, will count down to zero before the end of theTXOP 302, in an embodiment. On other hand, if the acknowledgement dataunit 416 is the last frame in transmitted in the TXOP 302, then thebackoff timer, set to the duration of EIFS based on detection of anerror in the acknowledgement frame 402, will not count down to zerobefore the end of the TXOP 302, thereby preventing the client stationthat received the acknowledgement data unit 416 in error from accessingthe medium after the end of the TXOP 302, in an embodiment. In anembodiment, to allow each client station 25 that is not an intendedrecipient of the acknowledgement data unit 416 to appropriately set itsNAV, the AP 14 selects, for transmission of the acknowledgement dataunit 416, a data rate, an MCS, and/or a Nss supported by all clientstations 25 in the WLAN 10. In an embodiment, to allow each clientstation 25 that is not an intended recipient of the acknowledgement dataunit 416 to appropriately set its NAV, the AP 14 selects, fortransmission of the acknowledgement data unit 416, a data rate, an MCS,and/or a Nss supported by all client stations 25 in the WLAN 10 if theacknowledgement data unit 416 is the last frame of the TXOP 302.

As an example, in an embodiment in which the acknowledgement data unit416 is a non-HT data unit, such as a data unit that conforms to the IEEE802.11a Standard, if the acknowledgement data unit 416 is not the lastframe to be transmitted in the TXOP 302, then the AP 14 selects, fortransmission of the acknowledgement data unit 416, a data rate from aset of data rates supported by the client stations 25 that are theintended recipients of the of the acknowledgement data unit 416. On theother hand, continuing with the same example, if the acknowledgementdata unit 416 is the last frame to be transmitted in the TXOP 302, theAP 14 selects, for transmission of the acknowledgement data unit 416, adata rate from a basic rate set of a basic service set (BSSBasicRateSet)of a BSS served by the AP 14, or, when the BSSBasicRateSet is empty oridle, selects a data rate from a setoff mandatory data rates supportedby the PHY processing unit 20 of the AP 14, in an embodiment.Accordingly, if the acknowledgement data unit 416 is the last frametransmitted in the TXOP 302, then all client stations 25 in the BSS areable to decode the acknowledgement data unit 416 for the purpose orsetting NAV based on a duration indication included in theacknowledgement data unit 416, in this embodiment.

As another example, in an embodiment in which the acknowledgement dataunit 416 is an HT data unit, such as a data unit that conforms to theIEEE 802.11n Standard, if the acknowledgement data unit 416 is not thelast frame to be transmitted in the TXOP 302, then the AP 14 selects,for transmission of the acknowledgement data unit 416, an MCS from a setof MCSs supported by the client stations 25 that are the intendedrecipients of the of the acknowledgement data unit 416. On the otherhand, continuing with the same example, if the acknowledgement data unit416 is the last frame to be transmitted in the TXOP 302, the AP 14selects, for transmission of the acknowledgement data unit 416, an MCSfrom a basic MCS set of a basic service set (BSSBasicMCSSet) of a BSSserved by the AP 14, or, when the BSSBasicMCSSet is empty or idle,selects an MCS from a set of mandatory MCSs supported by the PHYprocessing unit 20 of the AP 14, in an embodiment. Accordingly, if theacknowledgement data unit 416 is the last frame transmitted in the TXOP302, then all client stations 25 in the BSS are able to decode theacknowledgement data unit 416 for the purpose or setting NAV based on aduration indication included in the acknowledgement data unit 416, inthis embodiment.

As yet another example, in an embodiment in which the acknowledgementdata unit 416 is a VHT data unit, such as a data unit that conforms tothe IEEE 802.11ac Standard, the AP 14 selects, for transmission of theacknowledgement data unit 416, an MCS and Nss from a set of MCSs andnumbers of spatial streams supported by the client stations 25 that arethe intended recipients of the of the acknowledgement data unit 416. Onthe other hand, continuing with the same example, if the acknowledgementdata unit 416 is the last frame to be transmitted in the TXOP 302, theAP 14 selects, for transmission of the acknowledgement data unit 416, anMCS and an Nss from a basic set of VHT-MCS and Nss supported by a BSSserved by the AP 14, or, when the basic set of VHT-MCS and Nss is emptyor idle, selects an MCS and Nss from a mandatory set of MCS and Nsssupported by the PHY processing unit 20 of the AP 14, in an embodiment.Accordingly, if the acknowledgement data unit 416 is the last frametransmitted in the TXOP 302, then all client stations 25 in the BSS areable to decode the acknowledgement data unit 416 for the purpose orsetting NAV based on a duration indication included in theacknowledgement data unit 416, in this embodiment.

In an embodiment in which the acknowledgement data unit 416 is an HEdata unit, such as a data unit that conforms to the IEEE 802.11axStandard, the AP 14 selects, for transmission of the acknowledgementdata unit 416, an MCS and Nss from a set of MCSs and numbers of spatialstreams supported by the client stations 25 that are the intendedrecipients of the of the acknowledgement data unit 416.

In some embodiments, the acknowledge data unit 416 is included in, orcombined with, a multi-user (e.g., MU-MIMO of OFDMA) downlink datatransmission from the AP 14 to the client stations 25 during the TXOP302 or during another TXOP subsequent to the TXOP 302. That is, in suchembodiments, the downlink multi-user transmission includes both (i) theacknowledgement data unit 416 intended for the client stations 25 and(ii) respective data units, such as respective A-MPDUs, intended for theclient stations 25.

FIG. 5 is a diagram of an example control field 500 included in anacknowledgement data unit transmitted by the AP 14 to one or more clientstations 25. In an embodiment and/or scenario, the control field 500 isincluded in an acknowledgment data unit transmitted by the AP 14 to asingle client station 25 to acknowledge an uplink data unit received bythe AP from the single client station 25. In another embodiment and/orscenario, the control field 500 is included in an acknowledgment dataunit transmitted by the AP 14 to multiple client station 25 toacknowledge uplink data units simultaneously transmitted by the multipleclient stations 25 to the AP 14. In an embodiment and/or scenario, thecontrol field 500 is included in each acknowledgement data unit 310 ofFIG. 3 . In another embodiment and/or scenario, the control field 500 isincluded in the acknowledgement data unit 416 of FIG. 4 . In anotherembodiment and/or scenario, the control field 500 is included in asuitable acknowledgement frame different from the acknowledgement dataunits 310 or the acknowledgement data unit 416.

The control element 500 includes a plurality of fields 502. In theembodiment illustrated in FIG. 5 , the fields 502 include a framecontrol field 502-1, a duration/id field 502-2, a receiver address (RA)field 502-3, a transmitter address (TA) field 502-4, a BA control field502-5, a BA/Ack information field 502-6, and a frame sequence check(FCS) field 502-7. The number indicated in FIG. 5 above each of thefields 502 indicates the number of octets of bits in the correspondingfield 502, according to an example embodiment.

The RA field 502-3 includes an address of an intended receiver of theacknowledgement data unit that includes the control field 500, in anembodiment. In an embodiment and/or scenario in which the control field500 is included in a unicast acknowledgement data unit directed to onlyone client station 25, the RA field 502-3 includes a unicast address,such as a unicast MAC address, corresponding to the one client station25. On the other hand, in an embodiment and/or scenario in which thecontrol field 500 is included in a broadcast acknowledgement data unitdirected to multiple client stations 25, the RA field 502-3 includes abroadcast address, such as a broadcast MAC address, to indicate that theacknowledgement data unit is directed to multiple client stations 25.

FIG. 6 is a diagram illustrating bit allocation of a BA control field600 included in an acknowledgement data unit, according to anembodiment. The BA control field 600 corresponds to the BA control field502-5, in an embodiment. The BA control field 600 includes a pluralityof subfields 602. The subfields 602 collectively comprise 16 bits, inthe illustrated embodiment. The subfields 602 collectively comprise asuitable number of bits different than 16 bits, in other embodiments. Inthe embodiment illustrated in FIG. 6 , the BA control field 600 includesa BA Ack policy subfield 602-1, a multi-TID subfield 602-2, a compressedbitmap subfield 602-3, a GroupCast with Retries (GCR) subfield 602-4, agroup BA indication subfield 60205 a reserved subfield 602-6 and a TIDinformation subfield 602-7. Bit allocation for each of the subfields602, according to an example embodiment, is illustrated in FIG. 6 abovethe corresponding subfields 602.

In an embodiment, the group BA indication field 602-5 indicates whetherthe acknowledgement data unit that includes the BA control field 600includes a single acknowledgement to acknowledge a single data unitreceived from one client station 25 or includes multipleacknowledgements to acknowledge multiple data units received frommultiple client stations 25, for example as parts of an MU-MIMO uplinktransmission from the multiple client stations 25 or an OFDMAtransmission from the multiple client stations 25. In an embodiment, thegroup BA indication field 602-5 serves as an additional indication toindicate whether the acknowledgement data unit that includes the BAcontrol field 600 includes a single acknowledgement directed to oneclient station 25 or multiple acknowledgements directed to multipleclient stations 25, in addition to the indication provided by the RAfield 502-3 as discussed above with respect to FIG. 5 . In anotherembodiment, the group BA indication subfield 602-5 is omitted from theBA control field 600, and the RA field 502-3 is instead relied upon toindicate to indicate whether the acknowledgement data unit that includesthe BA control field 600 includes a single acknowledgement directed toone client station 25 or multiple acknowledgements directed to multipleclient stations 25.

FIG. 7 is a diagram of an example per-AID information element 700included in an acknowledgement data unit, according to an embodiment. Inan embodiment, one or more per-AID information elements 700 is/areincluded in the BA/Ack information field 502-6 of FIG. 5 . For example,the BA/Ack information field 502-6 includes a per-AID informationelement 700 corresponding to each client station 25 from which a dataunit 306 was received by the AP 14 in the uplink transmission 308 (FIG.3 ), in an embodiment. Accordingly, if the BA/Ack information field502-6 excludes a per-AID information element 700 corresponding to aparticular client station 25 that transmitted a data unit 306 as part ofthe uplink transmission 308, this indicates that the data unit 306 fromthe particular client station was not received by the AP 14, in anembodiment.

With continued reference to FIG. 7 , the per-AID information element 700includes fields 702, in an embodiment. The number indicated in FIG. 7above each of the fields 702 indicates the number of octets of bits inthe corresponding field 702, according to an example embodiment. In anembodiment, the per-AID information element 700 includes at least aper-AID information field 702-1. Several example embodiments of theper-AID information field 702-1 are described with respect to FIGS.8A-8B. Further, if the per-AID information element 700 includes a blockacknowledgement corresponding to multiple data units received from aclient station, then the per-AID information element 700 additionallyincludes a Block Ack starting sequence control field 702-2 and a BlockAck bitmap field 702-3, in an embodiment. On the other hand, if theper-AID information element 700 includes an acknowledgement thatacknowledges a single data unit received from a client station, them theper-AID information element 700 omits the BlockAck starting sequencecontrol field 702-2 and the BlockAck bitmap field 702-3, in anembodiment.

FIG. 8A is a diagram of an example per-AID information field 800,according to an embodiment. In an embodiment, the per-AID informationfield 800 corresponds to the per-AID information field 702-1. Theper-AID information field 800 is included in a per-AID informationelement that acknowledges a single data unit from a particular clientstation 25, or multiple data units, associated with a same trafficidentifier (TID), from a particular client station 25. The per-AIDinformation field 800 includes an identifier subfield 802-1, a reservedsubfield 802-2, and a BA/Ack subfield 802-3. The identified subfield802-1 identifies a client station for which the per-AID informationfield 800 is intended, in an embodiment. In an embodiment, theidentified subfield 802-1 includes at least a partial associationidentifier (AID) associated with the client station for which theper-AID information field 800 is intended. In another embodiment, theidentified subfield 802-1 includes another suitable identifier of theclient station for which the per-AID information field 800 is intended.

The BA/Ack indication field 802-3 indicates whether the per-AIDinformation element that includes the per-AID information field 800(e.g., the per-AID information element 700) includes (i) anacknowledgement that acknowledges a single data unit received from theclient station identified by the identifier field 802-1 or (ii) a blockacknowledgement that acknowledges multiple data units received from theclient station identified by the identifier field 802-1. In anembodiment, the BA/Ack indication field 802-3 comprises one bit. In anembodiment, a value of a logic zero (0) of the BA/Ack indication field802-3 indicates that the per-AID information element that includes theper-AID information field 800 (e.g., the per-AID information element700) includes an acknowledgement that acknowledges a single data unitreceived from the client station identified by the identifier field802-1, and a value of a logic one (1) of the BA/Ack indication field802-3 indicates that the per-AID information element that includes theper-AID information field 800 (e.g., the per-AID information element700) includes a block acknowledgement that acknowledges multiple dataunits received from the client station identified by the identifierfield 802-1. In another embodiment, a value of a logic one (1) of theBA/Ack indication field 802-3 indicates that the per-AID informationelement that includes the per-AID information field 800 (e.g., theper-AID information element 700) includes an acknowledgement thatacknowledges a single data unit received from the client stationidentified by the identifier field 802-1, and a value of a logic zero(0) of the BA/Ack indication field 802-3 indicates that the per-AIDinformation element that includes the per-AID information field 800(e.g., the per-AID information element 700) includes a blockacknowledgement that acknowledges multiple data units received from theclient station identified by the identifier field 802-1.

FIG. 8B is a diagram of an example per-AID information field 850,according to another embodiment. In an embodiment, the per-AIDinformation field 850 corresponds to the per-AID information field702-1. The per-AID information field 850 is included in a per-AIDinformation element that acknowledges multiple data units, associatedwith multiple traffic identifiers (TIDs), from a particular clientstation 25. In an embodiment, the per-AID information field 850 includesmultiple per-TID information fields, each per-TID information fieldcorresponding to a respective TID for which an acknowledgement is beingprovided. In an embodiment, each of the multiple information fieldsincludes an identifier subfield 852-1, a reserved subfield 852-2, and aBA/Ack subfield 852-3, and a TID subfield 852-4. The identified subfield852-1 identifies a client station for which the per-AID informationfield 800 is intended, in an embodiment. In an embodiment, theidentified subfield 852-1 includes at least a partial associationidentifier (AID) associated with the client station for which theper-AID information field 850 is intended. In an embodiment, theidentifier field 852-1 comprises fewer bits as compared to the number ofbits in the identifier field 802-1 of FIG. 8A. For example, whereas theidentifier field 802-1 of FIG. 8A comprises 12 bits, the identifierfield 852-1 comprises 9 bits, in an embodiment. In an embodiment inwhich the identifier field 852-1 includes a partial AID associated witha client station for which the per-AID information field 800 isintended, the identifier field 852-1 includes 9 bits (e.g., 9 mostsignificant bits, 9 least significant bits, or another suitable set of 9bits) of the AID associated with the client station. In anotherembodiment, the identifier field 852-2 is expanded to include bits oneor bits of there served subfield 852-2. For example, there servedsubfield 852-2 is omitted from the per-AID information field 850, andthe identifier field 852-1 is expanded to comprise 11 bits, in anembodiment.

The BA/Ack indication subfield 852-3 indicates whether the per-AIDinformation element that includes the per-AID information field 850(e.g., the per-AID information element 700 of FIG. 7 ) includes (i) anacknowledgement that acknowledges a single data unit associated with theindicated TID in the TID subfield 852-4, or a block acknowledgement thatacknowledges multiple data units associated with the indicated TID inthe TID subfield 852-4, in an embodiment. The BA/Ack indication subfield852-3 is generally the same as the BA/Ack indication subfield 802-3 ofFIG. 8A, in an embodiment.

Referring back to FIG. 7 , in an embodiment in which the BA/Ackindication 802-3 or the BA/Ack indication 852-3 indicates the per-AIDinformation element 700 includes a block acknowledgment thatacknowledges multiple data units, the Block Ack starting sequencecontrol field 702-2 indicates a sequence number corresponding to thefirst one of the data units being acknowledged, and each bit of theBlock Ack bitmap field 702-3 acknowledges a data unit with a sequencenumber that equals the sequence number indicated by the Block Ackstarting sequence control field 702-2 plus the index of the bit. Thus,for example, the first bit (bit index 0) of the Ack bitmap field 702-3acknowledges the data unit with the sequence number indicated by theBlock Ack starting sequence control field 702-2, the second bit (bitindex 1) Ack bitmap field 702-3 acknowledges the data unit with asequence number indicated by the Block Ack starting sequence controlfield 702-2 plus 1, etc., in an embodiment. In an embodiment, the valueof each bit of Ack bitmap field 702-3 indicates whether thecorresponding data unit was successfully received by the AP 14. Forexample, a value of logic one (1) of a bit of Ack bitmap field 702-3indicates that the corresponding data unit was successfully received bythe AP 14, and a value of logic zero (0) of a bit of Ack bitmap field702-3 indicates that the corresponding data unit was not successfullyreceived (e.g., not received or received with an error) by the AP 14.

FIG. 9 is a flow diagram of an example method 900 for simultaneouslycommunicating with multiple client devices in a WLAN, according to anembodiment. In an embodiment, the method 900 is implemented by an AP inthe WLAN, according to an embodiment. With reference to FIG. 1 , themethod 900 is implemented by the AP 14. For example, the method 900 isimplemented by the MAC processing unit 18 and/or by the PHY processingunit 20 of the AP 14, in an embodiment. In other embodiments, the method900 is implemented by other components of the AP 14, or is implementedby a suitable communication device other than the AP 14.

At block 902, multiple uplink data units simultaneously transmitted bymultiple client stations are received. In an embodiment, multiple dataunits 206 of FIGS. 2 and 3 are received. In an other embodiment,suitable data units different from the data units 206 of FIGS. 2 and 3are received. In an embodiment, the multiple client stations are membersof an MU-MIMO group, and the multiple data units are transmitted by themultiple client stations in respective spatial streams allocated to theclient stations. In another embodiment, the multiple client stations aremembers of an OFDMA group, and the multiple data units are transmittedby the multiple client stations in OFDM channels allocated to themultiple client stations.

At block 904, an acknowledgment data unit is generated. In anembodiment, the acknowledgement data unit acknowledges receipt of themultiple data units received at block 902. In an embodiment, theacknowledgement data unit includes (i) an indication that indicates thatthe acknowledgement data unit is intended for multiple client stationsand (ii) respective acknowledgement information for the multiple clientstations. In an embodiment, the acknowledgement data unit includes acontrol field such as the control field 500 of FIG. 5 . In anembodiment, the control field included in the acknowledgement data unitincludes the BA control field 600 of FIG. 6 and the BA/Ack informationelement 700 of FIG. 7 . In another embodiment, the acknowledgement dataunit includes other suitable control fields and/or other suitableinformation elements that acknowledge receipt of the multiple data unitreceived at block 902.

At block 906, the acknowledgement data unit generated at block 904 istransmitted to the multiple client stations from which the uplink dataunits were received at block 902.

FIG. 10 is a flow diagram of an example method 1000 for simultaneouslycommunicating with multiple client devices in a WLAN, according to anembodiment. In an embodiment, the method 1000 is implemented by an AP inthe WLAN, according to an embodiment. With reference to FIG. 1 , themethod 1000 is implemented by the AP 14, in an embodiment. For example,the method 1000 is implemented by the MAC processing unit 18 and/or bythe PHY processing unit 20 of the AP 14, in an embodiment. In otherembodiments, the method 1000 is implemented by other components of theAP 14, or is implemented by a suitable communication device other thanthe AP 14.

At block 1002, multiple uplink data units simultaneously transmitted bymultiple client stations are received. In an embodiment, multiple dataunits 206 of FIGS. 2 and 3 are received. In an other embodiment,suitable data units different from the data units 206 of FIGS. 2 and 3are received. In an embodiment, the multiple client stations are membersof an MU-MIMO group, and the multiple data units are transmitted by themultiple client stations in respective spatial streams allocated to theclient stations. In another embodiment, the multiple client stations aremembers of an OFDMA group, and the multiple data units are transmittedby the multiple client stations in OFDM channels allocated to themultiple client stations.

At block 1004, respective acknowledgment data units to acknowledgerespective data units received at block 1002 are generated. In anembodiment, each respective acknowledgement data unit includes (i) anindication that the acknowledgement data unit is directed to aparticular communication device of the multiple communication devicesfrom which the uplink data units are received at block 1002 and (ii)acknowledgement information for the particular communication device. Inan embodiment, the acknowledgement data units include respective controlfields such as the control field 500 of FIG. 5 . In an embodiment, therespective control fields included in the acknowledgement data unitsinclude respective BA control fields such as the BA control field 600 ofFIG. 6 and respective BA/Ack information elements such as the BA/Ackinformation elements 700 of FIG. 7 . In another embodiment, theacknowledgement data units include other suitable control fields and/orother suitable information elements that acknowledge receipt of themultiple data unit received at block 902.

At block 1006, an MU data unit that includes the respectiveacknowledgement data units generated at block 1004 is generated. In anembodiment and/or scenario, the MU data unit generated at block 1006 isan orthogonal frequency division multiple access (OFDMA) data unit thatincludes the respective acknowledgement data units in respectiveorthogonal frequency division multiplexing (OFDM) channels allocated tothe multiple communication devices. In another embodiment and/orscenario, the MU data unit generated at block 1006 is an MU-MIMO dataunit that includes the respective acknowledgement data units inrespective spatial streams allocated to the multiple secondcommunication devices. In an embodiment, the MU data unit 312 of FIG. 3is generated at block 1006. In another embodiment, a suitable MU dataunit different from the MU data unit 312 is generated at block 1006.

At block 1008, the MU data unit generated at block 1006 is transmittedto the multiple communication devices.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

In an embodiment, a method for simultaneously communicating withmultiple communication devices in a wireless local area network includesreceiving, at a first communication device, a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices. The method also includes generating, at the first communicationdevice, an acknowledgement data unit to acknowledge receipt of themultiple data units simultaneously transmitted by multiple secondcommunication devices, wherein the acknowledgement data unit includes(i) an indication that indicates that the acknowledgement data unit isintended for multiple second communication devices and (ii) respectiveacknowledgement information for the multiple second communicationdevices. The method additionally includes causing the acknowledgementdata unit to be transmitted from the first communication device to themultiple second communication devices.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

The multiple second communication devices are included in a multi-usermultiple input multiple output (MU-MIMO) group.

Receiving, at the first communication device, a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices comprises receiving a plurality of data units transmitted inrespective spatial streams respectively allocated to the multiple secondcommunication devices.

The multiple second communication devices are included in an orthogonalfrequency division multiple access (OFDMA) group.

Receiving, at the first communication device, a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices comprises receiving a plurality of data units simultaneouslytransmitted in respective orthogonal frequency division multiplexing(OFDM) channels allocated to the multiple second communication devices.

The acknowledgement data unit includes a broadcast receiver address, andwherein the broadcast receiver address serves as the indication that theacknowledgement data unit is intended for multiple second communicationdevices.

The respective acknowledgement information for the multiple secondcommunication devices includes, for each of the multiple secondcommunication devices, (i) a respective identifier associated with thesecond communication device and (ii) an indication of whether theacknowledgement data unit includes (a) an acknowledgement thatacknowledges a single data unit received from the second communicationdevice or (b) a block acknowledgement that acknowledges multiple dataunits received from the second communication device.

The respective identifier associated with the second communicationdevice is an association identifier (AID) associated with the secondcommunication device.

The respective identifier associated with the second communicationdevice is a partial association identifier (AID) associated with thesecond communication device.

The respective acknowledgement information for the multiple secondcommunication devices further includes, for at least one of the multiplesecond communication devices, an indication that the acknowledgementinformation correspond to the at least one second communication deviceincludes multiple acknowledgements for data units corresponding tomultiple traffic identifiers.

The method further includes selecting, at the first communication, oneor more of (i) a data rate, (ii) modulation and coding scheme (MCS) and(iii) number of spatial streams (Nss) to be used for transmission of theacknowledgement data unit to the second communication devices, whereinthe one or more of (i) a data rate, (ii) modulation and coding scheme(MCS) and (iii) number of spatial streams (Nss) are selected withoutconsidering corresponding one or more parameters of the received uplinkdata units.

The method further includes, prior to receiving the plurality of uplinkdata units simultaneously transmitted by multiple second communicationdevices, transmitting, by the first communication device, a controlframe that prompts transmission of the plurality of uplink data units bythe second communication devices.

In another embodiment a first communication device comprises a networkinterface having one or more integrated circuits. The one or moreintegrated circuits are configured to receive a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices. The one or more integrated circuits are also configured togenerate an acknowledgement data unit to acknowledge receipt of themultiple data units simultaneously transmitted by multiple secondcommunication devices, wherein the acknowledgement data unit includes(i) an indication that indicates that the acknowledgement data unit isintended for multiple second communication devices and (ii) respectiveacknowledgement information for the multiple second communicationdevices. The one or more integrated circuits are additionally configuredto cause the acknowledgement data unit to be transmitted from the firstcommunication device to the multiple second communication devices.

In other embodiments, the first communication device includes anysuitable combination of one or more of the following features.

The multiple second communication devices are included in a multi-usermultiple input multiple output (MU-MIMO) group.

The one or more integrated circuits are configured to receive theplurality of data units transmitted in respective spatial streamsrespectively allocated to the multiple second communication devices.

The multiple second communication devices are included in an orthogonalfrequency division multiple access (OFDMA) group.

The one or more integrated circuits are configured to receive theplurality of data units transmitted in respective orthogonal frequencydivision multiplexing (OFDM) channels allocated to the multiple secondcommunication devices.

The acknowledgement data unit includes a broadcast receiver address, andwherein the broadcast receiver address serves as the indication that theacknowledgement data unit is intended for multiple second communicationdevices.

The respective acknowledgement information for the multiple secondcommunication devices includes, for each of the multiple secondcommunication devices, (i) a respective identifier associated with thesecond communication device and (ii) an indication of whether theacknowledgement data unit includes (a) an acknowledgement thatacknowledges a single data unit received from the second communicationdevice or (b) a block acknowledgement that acknowledges multiple dataunits received from the second communication device.

The respective identifier associated with the second communicationdevice is an association identifier (AID) associated with the secondcommunication device.

The respective identifier associated with the second communicationdevice is a partial association identifier (AID) associated with thesecond communication device.

The respective acknowledgement information for the multiple secondcommunication devices further includes, for at least one of the multiplesecond communication devices, an indication that the acknowledgementinformation correspond to the at least one second communication deviceincludes multiple acknowledgements for data units corresponding tomultiple traffic identifiers.

The one or more integrated circuits are further configured to select oneor more of (i) a data rate, (ii) modulation and coding scheme (MCS) and(iii) number of spatial streams (Nss) to be used for transmission of theacknowledgement data unit to the second communication devices, whereinthe one or more of (i) a data rate, (ii) modulation and coding scheme(MCS) and (iii) number of spatial streams (Nss) are selected withoutconsidering corresponding one or more parameters of the received uplinkdata units.

The one or more integrated circuits are further configured to, prior toreceiving the plurality of uplink data units simultaneously transmittedby multiple second communication devices, transmit a control frame thatprompts transmission of the plurality of uplink data units by the secondcommunication devices.

In another embodiment, a method for simultaneously communicating withmultiple communication devices in a wireless local area network includesreceiving, at a first communication device, a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices. The method also includes generating, at the first communicationdevice, respective acknowledgment data units to acknowledge respectiveuplink data units received from the multiple second communicationdevices. The method additionally includes generating one of (i) anorthogonal frequency division multiple access (OFDMA) data unit thatincludes the respective acknowledgement data units in respectiveorthogonal frequency division multiplexing (OFDM) channels allocated tothe multiple second communication devices or (ii) a multiuser multipleinput multiple output (MU-MIMO) data unit that includes the respectiveacknowledgement data units in respective spatial streams allocated tothe multiple second communication devices. The method further includescausing the generated one of (i) the OFDMA data unit or (ii) the MU-MIMOdata unit to be transmitted from the first communication device to themultiple second communication devices.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

The multiple second communication devices are included in a multi-usermultiple input multiple output (MU-MIMO) group.

The multiple second communication devices are included in a multi-usermultiple input multiple output (MU-MIMO) group.

Receiving, at the first communication device, a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices comprises receiving a plurality of data units transmitted inrespective spatial streams respectively allocated to the multiple secondcommunication devices.

The multiple second communication devices are included in an orthogonalfrequency division multiple access (OFDMA) group.

Receiving, at the first communication device, a plurality of uplink dataunits simultaneously transmitted by multiple second communicationdevices comprises receiving a plurality of data units simultaneouslytransmitted in respective orthogonal frequency division multiplexing(OFDM) channels allocated to the multiple second communication devices.

The method further includes padding one or more of the respectiveacknowledgement data units to equalize lengths of the respectiveacknowledgement data units.

In still another embodiment, a first communication device comprises anetwork interface having one or more integrated circuits. The one ormore integrated circuits are configured to receive a plurality of uplinkdata units simultaneously transmitted by multiple second communicationdevices. The one or more integrated circuits are also configured togenerate respective acknowledgment data units to acknowledge respectiveuplink data units received from the multiple second communicationdevices. The one or more integrated circuits are additionally configuredto generate one of (i) an orthogonal frequency division multiple access(OFDMA) data unit that includes the respective acknowledgement dataunits in respective orthogonal frequency division multiplexing (OFDM)channels allocated to the multiple second communication devices or (ii)a multi user multiple input multiple output (MU-MIMO) data unit thatincludes the respective acknowledgement data units in respective spatialstreams allocated to the multiple second communication devices. The oneor more integrated circuits are additionally configured to cause thegenerated one of (i) the OFDMA data unit or (ii) the MU-MIMO data unitto be transmitted from the first communication device to the multiplesecond communication devices.

In other embodiments, the first communication device includes anysuitable combination of one or more of the following features.

The multiple second communication devices are included in a multi-usermultiple input multiple output (MU-MIMO) group.

The one or more integrated circuits are configured to receive theplurality of data units transmitted by the multiple second communicationdevices using respective spatial streams respectively allocated to themultiple second communication devices.

The multiple second communication devices are included in an orthogonalfrequency division multiple access (OFDMA) group.

The one or more integrated circuits are configured to receive theplurality of data units transmitted by the multiple second communicationdevices in respective orthogonal frequency division multiplexing (OFDM)channels allocated to the multiple second communication devices.

The one or more integrated circuits are further configured to pad one ormore of the respective acknowledgement data units to equalize lengths ofthe respective acknowledgement data units.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for simultaneously communicating withmultiple communication devices in a wireless local area network, themethod comprising: receiving, at a first communication device, aplurality of uplink data units simultaneously transmitted by multiplesecond communication devices of a multi-user multiple input multipleoutput (MU-MIMO) group or of an orthogonal frequency division multipleaccess (OFDMA) group; generating, at the first communication device, anacknowledgement data unit to acknowledge receipt of the multiple dataunits simultaneously transmitted by multiple second communicationdevices, wherein the acknowledgement data unit includes (i) anindication that indicates that the acknowledgement data unit is intendedfor multiple second communication devices and (ii) respectiveacknowledgement information for the multiple second communicationdevices; wherein the acknowledgement data unit includes a control fieldthat includes a frame control field, a duration/id field, a receiveraddress field, a transmitter address field, a BA control field a BA/Ackinformation field, and a frame sequence check field; wherein theindication that indicates that the acknowledgement data is intended formultiple second communication devices is in the BA/Ack informationfield.
 2. The method of claim 1, wherein the multiple secondcommunication devices are included in a multi-user multiple inputmultiple output (MU-MIMO) group, and receiving, at the firstcommunication device, a plurality of uplink data units simultaneouslytransmitted by multiple second communication devices comprises receivinga plurality of data units transmitted in respective spatial streamsrespectively allocated to the multiple second communication devices. 3.The method of claim 1, wherein the multiple second communication devicesare included in an orthogonal frequency division multiple access (OFDMA)group, and receiving, at the first communication device, a plurality ofuplink data units simultaneously transmitted by multiple secondcommunication devices comprises receiving a plurality of data unitssimultaneously transmitted in respective orthogonal frequency divisionmultiplexing (OFDM) channels allocated to the multiple secondcommunication devices.
 4. The method of claim 1, wherein theacknowledgement data unit includes a broadcast receiver address, andwherein the broadcast receiver address serves as the indication that theacknowledgement data unit is intended for multiple second communicationdevices.
 5. The method of claim 1, wherein the respectiveacknowledgement information for the multiple second communicationdevices includes, for each of the multiple second communication devices,(i) a respective identifier associated with the second communicationdevice and (ii) an indication of whether the acknowledgement data unitincludes (a) an acknowledgement that acknowledges a single data unitreceived from the second communication device or (b) a blockacknowledgement that acknowledges multiple data units received from thesecond communication device.
 6. The method of claim 5, wherein therespective identifier associated with the second communication device isan association identifier (AID) associated with the second communicationdevice.
 7. The method of claim 5, wherein the respective identifierassociated with the second communication device is a partial associationidentifier (AID) associated with the second communication device.
 8. Themethod of claim 1, further comprising, prior to receiving the pluralityof uplink data units simultaneously transmitted by multiple secondcommunication devices, transmitting, by the first communication device,a control frame that prompts transmission of the plurality of uplinkdata units by the second communication devices.
 9. A first communicationdevice, comprising: a network interface having one or more integratedcircuits configured to receive a plurality of uplink data unitssimultaneously transmitted by multiple second communication devices,generate an acknowledgement data unit to acknowledge receipt of themultiple data units simultaneously transmitted by multiple secondcommunication devices, wherein the acknowledgement data unit includes(i) an indication that indicates that the acknowledgement data unit isintended for multiple second communication devices; wherein theacknowledgement data unit includes a control field that includes a framecontrol field a duration/id field, a receiver address field, atransmitter address field, a BA control field, a BA/Ack informationfield, and a frame sequence check field; wherein the indication thatindicates that the acknowledgement data is intended for multiple secondcommunication devices is in the BA/Ack information field.
 10. The firstcommunication device of claim 9, wherein the multiple secondcommunication devices are included in a multi-user multiple inputmultiple output (MU-MIMO) group, and the one or more integrated circuitsare configured to receive the plurality of data units transmitted inrespective spatial streams respectively allocated to the multiple secondcommunication devices.
 11. The first communication device of claim 9,wherein the multiple second communication devices are included in anorthogonal frequency division multiple access (OFDMA) group, and the oneor more integrated circuits are configured to receive the plurality ofdata units transmitted in respective orthogonal frequency divisionmultiplexing (OFDM) channels allocated to the multiple secondcommunication devices.
 12. The first communication device of claim 9,wherein the acknowledgement data unit includes a broadcast receiveraddress, and wherein the broadcast receiver address serves as theindication that the acknowledgement data unit is intended for multiplesecond communication devices.
 13. The first communication device ofclaim 9, wherein the respective acknowledgement information for themultiple second communication devices includes, for each of the multiplesecond communication devices, (i) a respective identifier associatedwith the second communication device and (ii) an indication of whetherthe acknowledgement data unit includes (a) an acknowledgement thatacknowledges a single data unit received from the second communicationdevice or (b) a block acknowledgement that acknowledges multiple dataunits received from the second communication device.
 14. The firstcommunication device of claim 13, wherein the respective identifierassociated with the second communication device is an associationidentifier (AID) associated with the second communication device. 15.The first communication device of claim 13, wherein the respectiveidentifier associated with the second communication device is a partialassociation identifier (AID) associated with the second communicationdevice.